libvirt's "host-passthrough" uses "-cpu host', and it "-cpu host" enables every feature that can be enabled on the host. From my test results, I found that even when use host-passthrough mode, VM's cpu features are very different from host, this doesn't match what host-passthrough mode's explanation.
libvirt's option exlanation: With this mode, the CPU visible to the guest should be exactly the same as the host CPU even in the aspects that libvirt does not understand.
If the behavior of "-cpu host" doesn't match libvirt expectations, we need to clarify what are the requirements, and maybe have a "try to be close to host CPU mode" as opposed to the current "enable everything that can be enabled" mode. Does the results above indicates what you mean to do? or the current way doesn't work as we expect.
Thanks!